# Habitable zone around a Blue Supergiant

I am writing a story centered around a planet orbiting a Blue Supergiant star. What I want to know is how far away a planet would have to be to be in the habitable zone of such a star. The star I have in mind is roughly comparable to Rigel and don't mind anything like the need for protection from radiation, the race that inhabits this world can handle radiation and the likes of solar flares to the point they basically thrive in radiation that would utterly destroy a human.

Some side questions I have are these:

• How many Earth years would 1 year on this planet be?

• Would the 4 seasons still be roughly equally divided in that year?

• Just to clarify, the question of whether or not a planet could develop life in the lifespan of a blue supergiant does not matter. I merely want to know how far away the planet would have to be to be in the habitable zone of such a star (i know every star type has a habitable zone) and if the 4 seasons would still be equally divided over the year like on earth. Commented Nov 6, 2018 at 13:14

Ok, so using Rigel as an example:

Rigel has a luminosity of 120,000 sols, so for a planet to receive the same insolation as the Earth does around the sun, it would orbit at a distance of 346.4 AU.

Given a stellar mass of 23 sols, and a planetary mass of 1 Earth, the year length is 1344.09 Earth years.

Seasons are tricky since they have to do with the axial tilt of the planet, and given the year length, precession could actually cause the seasons to shift within that time.

You should also be aware that the spectrum of the host star has an effect of the strength of ice albedo feedback in the climate of planets. It is possible that around a Blue Giant, that more of the total insolation would be reflected back into space, so this hypothetical planet could very well be an irradiated snowball.

Reference: https://arxiv.org/abs/1305.6926

• Math checks out, good answer! Commented Nov 5, 2018 at 21:26
• When you want four seaons still, you could make an not linear spin, which tilts the axis over months
– user55267
Commented Nov 6, 2018 at 8:50
• @Arkenstein XII I know this is an old question but what would the sun of that hypothetical planet look like? Would it look similar to our sun or be a visibly blue color? Commented May 2, 2020 at 14:10

Note that the lifespan of the star is going to factor here. Rigel is estimated to be only about 10 million years old and will go kablooey in a supernova within the next few million years. That makes the odds of any life-bearing planets around any similar star extremely slim and unlikely as they'd barely have time to finish cooling to a temperature to support life before the big bang. Earth took a few hundred million years before it did it.

• It makes the odds of life-bearing worlds basically zero. 10 million years from the ignition of the sun the Earth was still being bombarded. Commented Nov 6, 2018 at 9:58
• Yes, but really advanced civilizations could move planets from other stars into the Rigel system and terraform them if they have a reason to. Commented Nov 6, 2018 at 17:11